This invention relates to a method for treating contact lenses and more particularly to a method for modifying the surface of hard contact lenses so as to render the lenses more compatible with eye fluids.
The contact lenses to which use of this invention is directed are those known as hard lenses which are usually manufactured of transparent methyl methacrylate polymer. Such lenses as presently used are generally of the non-scleral or corneal type which fit directly on the cornea of the eye. One side of the lens is in full contact with the eye fluids while the other, or outer, side is in intermittant contact with the eye lid during eye closure as in blinking.
While the methyl methacrylate polymer lenses solved a number of problems inherent in older style lenses, being unbreakable and comparatively easy to insert, new problems were introduced because of the inherent nature of methyl methacrylate polymers. Manufacture of methyl methacrylate contact lenses is generally accomplished by a first rough grinding with steel and a final grinding with abrasive powders. The resulting lens surfaces display hydrophobic properties which are considered to be caused both by the general properties of the plastic and by the surface changes induced through grinding. Consequently, the lens surfaces are poorly wet by the eye fluids and the outer surface of the lens has a tendency to dry between applications of lacrimal fluid by the eye lids during blinking. This drying phenomenon often causes irritation and discomfort to the wearer and can even cause interference with vision.
There have been a number of ophthalmic solutions developed to act as wetting, cushioning or lubricating agents for contact lenses. These solutions are formulated to be compatible with the natural eye fluids and to enhance the wetting properties of eye fluids toward plastic contact lenses. Generally such ophthalmic solutions are isotonic, buffered to an appropriate pH, sterile and contain additives such as wetting agents, viscosity modifiers and medicaments. The solutions tend to function as artificial tears and provide wetting and lubricating effects toward contact lenses superior to the natural eye fluids. One example of such ophthalmic solutions is disclosed in U.S. Pat. No. 3,856,919.
Use of wetting and cushioning solutions provides a high degree of comfort to most wearers of contact lenses. Some individuals, however, suffer from overawareness of the lens presence. This problem is generally most acute upon initial wearing and the awareness typically subsides with time. In others, the problem does not subside and results in chronic overawareness which may even lead to an inability to continue wearing contact lenses. Consequently, there has been a persistent need for methods to give a contact lens wearer more comfort particularly during the initial wearing period.
It has been recognized in printed circuit manufacture, in the preparation of synthetic fibers for dyeing, in the production of photographic films and like uses, that an aqueous suspension of hydrous oxides will enhance the wettability of solid surfaces. Such techniques are disclosed in U.S. Pat. No. 3,657,003. It is also known that surface treatment of solids with inorganic colloid increases the strength of an adhesive band. This is disclosed in U.S. Pat. No. 3,861,978. Additionally, U.S. Pat. No. 3,854,952 discloses a silver halide carried on colloidal particles of an inorganic hydrous oxide to form photosensitive films or sheets.